Magnetic floating gate memory

ABSTRACT

An apparatus includes at least one memory device including a floating gate element and a magnetic field generator that operably applies a magnetic field to the memory device. The magnetic field directs electrons in the memory device into the floating gate element.

BACKGROUND

Field-effect transistors (FET) has been considered to be an idealtechnology for nonvolatile memory because of its random access, highspeed, low power, high density and simplicity. For a nonvolatilesemiconductor storage device in which each memory cell is composed of anFET provided with a floating gate covered by an insulating film and usedas a charge storing layer, data is stored by controlling the amount ofelectrons stored in the floating gate thereby changing the thresholdvoltage of the transistor. When programming or erasing data into or fromthe memory cell, electrons are either injected or ejected from thefloating gate via the insulating film.

Electron injection/ejection is possible by using the (Fowler-Nordheim(F-N)) tunnel phenomenon and the hot electron phenomenon. Electrons areinjected in the insulating film around the floating gate with theapplication of a high electrical field. In the case of hot electroninjection, an electric field between a source region and drain region ofa MOSFET semiconductor memory device accelerates electrons travelingbetween the source and drain regions to a velocity where these electronsare termed “hot” electrons. To attract these hot electrons, a floatinggate of the FET is biased at a high voltage through a control gate ofthe FET. As the hot electrons move very fast, their travel time beneaththe floating gate of the FET is too short to attract many of the hotelectrons into the floating gate of the FET. Thus, electron injectionvia hot electron injection is not very efficient.

BRIEF SUMMARY

The present disclosure relates to magnetic floating gate memory withimproved electron injection efficiency. In particular the presentdisclosure relates to magnetic floating gate memory that generates amagnetic field that is perpendicular to a hot electron travel directionbetween a source region and a drain region and perpendicular to a hotelectron injection direction. The magnetic field bends the hot electrontravel direction by a Lorentz's force, directing it into the floatinggate of a FET through the hot electron injection direction.

A memory device includes a substrate having a source region, a drainregion and a channel region. The channel region separates the sourceregion and the drain region. Electrons flow through the channel regionbetween the source region and the drain region in a horizontaldirection. An electrically insulating layer is adjacent to the sourceregion, drain region and channel region. A floating gate element isadjacent to the electrically insulating layer. The electricallyinsulating layer separates the floating gate element from the channelregion. A control gate electrode is adjacent to the floating gateelement. The floating gate element separates the control gate electrodefrom the electrically insulating layer. The channel region, electricallyinsulating layer, floating gate element and control gate electrode arestacked in a vertical direction. The vertical direction is perpendicularto the horizontal direction. A magnetic field is directed through thechannel region and is perpendicular to the vertical direction and thehorizontal direction.

One illustrative method of writing to floating gate memory deviceincludes applying a magnetic field through a floating gate memory deviceto direct electrons in the device into a floating gate element of thefloating gate memory device.

Another illustrative memory device includes a substrate having a sourceregion, a drain region and a channel region. The channel regionseparates the source region and the drain region and electrons flowthrough the channel region between the source region and the drainregion. An electrically insulating layer is adjacent to the sourceregion, drain region and channel region. A floating gate element isadjacent to the electrically insulating layer, and the electricallyinsulating layer separates the floating gate element from the channelregion. A control gate electrode is adjacent to the floating gateelement. The floating gate element separates the control gate electrodefrom the electrically insulating layer. The channel region, electricallyinsulating layer, floating gate element and control gate electrode arestacked in a vertical direction. A plurality of magnetic particles arewithin the channel region.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of an illustrative floatinggate memory device with a magnetic field directed through a channelregion of the floating gate memory device;

FIG. 2 is a diagram of forces acting on a hot electron in a channelregion of the floating gate memory device illustrated in FIG. 1;

FIG. 3 is a schematic cross-sectional view of an illustrative floatinggate memory device with a magnetic floating gate element;

FIG. 4 is a schematic cross-sectional view of an illustrative floatinggate memory device with an adjacent magnetic element;

FIG. 5 is a schematic cross-sectional view of an illustrative floatinggate memory device with an adjacent magnetic field generating electriccoil;

FIG. 6 is a schematic cross-sectional view of an illustrative floatinggate memory device with magnetic particles in a channel region of afloating gate memory device; and

FIG. 7 is a flow diagram of an illustrative method for writing to afloating gate memory device.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.The definitions provided herein are to facilitate understanding ofcertain terms used frequently herein and are not meant to limit thescope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

The present disclosure relates to magnetic floating gate memory. Thememory apparatus includes at least one memory device including afloating gate element and a magnetic field generator that operablyapplies a magnetic field to the memory device. The magnetic fielddirects electrons in the memory device into the floating gate element.In particular the present disclosure relates to magnetic floating gatememory that generates a magnetic field that is perpendicular to a hotelectron travel direction between a source region and a drain region andperpendicular to a hot electron injection direction. The magnetic fieldbends the hot electron direction by a Lorentz's force, directing it intothe floating gate of a FET. While the present disclosure is not solimited, an appreciation of various aspects of the disclosure will begained through a discussion of the examples provided below.

FIG. 1 is a schematic cross-sectional view of an illustrative floatinggate memory device 10 with a magnetic field MF directed thought achannel region 11 of the floating gate memory device 10. FIG. 2 is adiagram of forces acting on a hot electron e⁻ in a channel region 11 ofthe floating gate memory device 10 illustrated in FIG. 1.

The memory device 10 includes a substrate 12 having a source region S, adrain region D and a channel region 11. The channel region 11 separatesthe source region S and the drain region D. Electrons e⁻ flow throughthe channel region 11 between the source region S and the drain region Din a horizontal direction (illustrated in FIG. 2 with the velocity arrowdirected to the right) or along the x-axis. An electrically insulatinglayer 13 is adjacent to the source region S, drain region D and channelregion 11. A floating gate element FG is adjacent to the electricallyinsulating layer 13. The electrically insulating layer 13 separates thefloating gate element FG from the channel region 11. A control gateelectrode CG is adjacent to the floating gate element FG. The floatinggate element FG separates the control gate electrode CG from theelectrically insulating layer 13. The channel region 11, electricallyinsulating layer 13, floating gate element FG and control gate electrodeCG are stacked in a vertical direction (illustrated in FIG. 2 with theLorentz force arrow) or along the y-axis. The vertical direction(y-axis) is perpendicular to the horizontal direction (x-axis).

A magnetic field MF is directed through the channel region 11 andperpendicular to the vertical direction (y-axis) and the horizontaldirection (x-axis or hot electron travel velocity direction). The term“perpendicular” refers to ±10 degrees of 90 degrees, throughout thisapplication. The magnetic field MF is illustrated as coming out of thepage along the z-axis. The magnetic field MF generates a Lorentz forceon the hot electrons e⁻ flowing from the source region S toward thedrain region D when a voltage V₁ is applied to the control gateelectrode CG and a voltage V₂ is applied to the drain region D. TheLorentz force alters the hot electron travel direction or trajectory,bending it toward the floating gate element FG. The Lorentz force isproportional to the electron's speed. The Lorentz force improves theefficiency of the hot electron injection rate into the floating gateelement FG, thus improving the write speed of the floating gate elementFG.

FIG. 3 is a schematic cross-sectional view of an illustrative floatinggate memory device with a magnetic floating gate element MFG. A memorydevice 20 includes a substrate 22 having a source region S, a drainregion D and a channel region 21. The channel region 21 separates thesource region S and the drain region D. Electrons e⁻ flow through thechannel region 21 between the source region S and the drain region D ina horizontal direction along the x-axis (as illustrated in FIG. 2). Anelectrically insulating layer 23 is adjacent to the source region S,drain region D and channel region 21. A magnetic floating gate elementMFG is adjacent to the electrically insulating layer 23. Theelectrically insulating layer 23 separates the magnetic floating gateelement MFG from the channel region 21. A control gate electrode CG isadjacent to the magnetic floating gate element MFG. The magneticfloating gate element MFG separates the control gate electrode CG fromthe electrically insulating layer 23. The channel region 21,electrically insulating layer 23, magnetic floating gate element MFG andcontrol gate electrode CG are stacked in a vertical direction along they-axis (as illustrated in FIG. 2). The vertical direction (y-axis) isperpendicular to the horizontal direction (x-axis).

The magnetic floating gate element MFG generates a magnetic field MFthat is directed through the channel region 21 and perpendicular to thevertical direction (y-axis) and the horizontal direction (x-axis or hotelectron travel direction). The magnetic field MF is illustrated ascoming out of the page along the z-axis. The magnetic field MF generatesa Lorentz force on the hot electrons e⁻ flowing from the source region Stoward the drain region D when a voltage V₁ is applied to the controlgate electrode CG and a voltage V₂ is applied to the drain region D. TheLorentz force alters the electron trajectory, bending it toward thefloating gate element FG. The Lorentz force is proportional to theelectron's speed. The Lorentz force improves the efficiency of the hotelectron injection rate into the floating gate element FG, thusimproving the write speed of the floating gate element FG.

The magnetic floating gate element MFG includes a ferromagnetic layer FMthat generates the magnetic field MF described above. The ferromagneticlayer FM can be located proximate to the channel region 21. Theferromagnetic layer FM can be formed of any useful ferromagneticmaterial or alloy such as, for example, Fe, Co, and/or Ni. In manyembodiments the ferromagnetic layer FM is located a linear distance ofless than 200 Angstroms, or less than 100 Angstroms, or less than 50Angstroms from the channel region 21. In many of these embodiments, thecontrol gate electrode CG is a non-magnetic element.

In some embodiments the magnetic floating gate element MFG also includesan antiferromagnetic pinning layer AFM to assist in stabilizing themagnetic field MF generated by the ferromagnetic layer FM. Theantiferromagnetic pinning layer AFM can be formed of any usefulantiferromagnetically ordered material such as, for example, PtMn, IrMnand others. In other embodiments the magnetic floating gate element MFGincludes a synthetic antiferromagnetic element or a syntheticantiferromagnetic and an antiferromagnetic pinning layer.

FIG. 4 is a schematic cross-sectional view of an illustrative floatinggate memory device 10 with an adjacent magnetic element 30. The floatinggate memory device 10 is described in relation to FIG. 1 and FIG. 2above. A magnetic element 30 generates the magnetic field MF through thechannel region and perpendicular to the vertical direction (y-axis) andthe horizontal direction (x-axis or hot electron travel direction), asdescribed above. The magnetic element 30 can be any useful magneticelement such as, for example, a permanent magnetic (as illustrated witha North Pole N and a South Pole S). The adjacent magnetic element 30 isproximate to the floating gate memory device 10 but separate from thefloating gate memory device 10 so that the magnetic element 30 generatesthe magnetic field MF through the channel region of the floating gatememory device 10. The magnetic element 30 can be thick enough to producea strong fringe magnetic field, and can be a soft magnetic layerstabilized with an antiferromagnetic pinning layer and/or syntheticantiferromagnetic element, as described above.

FIG. 5 is a schematic cross-sectional view of an illustrative floatinggate memory device 10 with an adjacent magnetic field generatingelectric coil 40. The floating gate memory device 10 is described inrelation to FIG. 1 and FIG. 2 above. The electric coil 40 generates themagnetic field MF through the channel region and perpendicular to thevertical direction (y-axis) and the horizontal direction (x-axis or hotelectron travel direction), as described above. The electric coil 40 canbe formed of any useful electrically conductive wire, with or withouthigh permeability core layers. The electric coil 40 is proximate to thefloating gate memory device 10 but separate from the floating gatememory device 10 so that the electric coil 40 generates the magneticfield MF through the channel region of the floating gate memory device10. The electric coil 40 is illustrated as a plurality of wire windingdirected into the page above the floating gate memory device 10 anddirected out of the page below the floating gate memory device 10.

FIG. 6 is a schematic cross-sectional view of an illustrative floatinggate memory device with magnetic particles M_(P) in a channel region 51of a floating gate memory device 50. The memory device 50 includes asubstrate 52 having a source region S, a drain region D and a channelregion 51. The channel region 51 separates the source region S and thedrain region D. Electrons e⁻ flow through the channel region 51 betweenthe source region S and the drain region D in a horizontal direction(illustrated with the velocity arrow directed to the right) or along thex-axis (as illustrated in FIG. 2). An electrically insulating layer isadjacent to the source region S, drain region D and channel region 51. Afloating gate element FG is adjacent to the electrically insulatinglayer. The electrically insulating layer separates the floating gateelement FG from the channel region 51. A control gate electrode CG isadjacent to the floating gate element FG. The floating gate element FGseparates the control gate electrode CG from the electrically insulatinglayer. The channel region 51, electrically insulating layer, floatinggate element FG and control gate electrode CG are stacked in a verticaldirection along the y-axis (as illustrated in FIG. 2). The verticaldirection (y-axis) is perpendicular to the horizontal direction(x-axis).

A plurality of magnetic particles M_(P) are disposed within the channelregion 51 of a floating gate memory device 50. The magnetic particlesM_(P) have an average lateral size in a range from 1 to 6 nanometers orfrom 2 to 5 nanometers. The magnetic particles M_(P) can be formed ofany useful ferromagnetic material such as, for example, nickel orcobalt. The magnetic particles M_(P) can be doped into the channelregion 51 of floating gate memory device 50 substrate 52 using knownsemiconductor fabrication doping methods.

The magnetic particles M_(P) generate local magnetic fields that apply aLorentz force on hot electrons passing thorough the channel region 51that alters the hot electron travel direction or trajectory, bending ittoward the floating gate element FG. The Lorentz force is proportionalto the electron's speed. The Lorentz force improves the efficiency ofthe hot electron injection rate into the floating gate element FG, thusimproving the write speed of the floating gate element FG.

FIG. 7 is a flow diagram of an illustrative method for writing to afloating gate memory device 100. The method includes generating a flowof hot electrons through a channel region of a floating gate memorydevice substrate, at block 101. Then the method includes applying amagnetic field through the channel region, the magnetic field directingthe hot electrons into a floating gate element of the floating gatememory device.

Thus, embodiments of the MAGNETIC FLOATING GATE MEMORY are disclosed.The implementations described above and other implementations are withinthe scope of the following claims. One skilled in the art willappreciate that the present disclosure can be practiced with embodimentsother than those disclosed. The disclosed embodiments are presented forpurposes of illustration and not limitation, and the present inventionis limited only by the claims that follow.

1. A memory device comprising: a substrate having a source region, adrain region and a channel region, the channel region separates thesource region and the drain region, electrons flow through the channelregion between the source region and the drain region in a horizontaldirection; an electrically insulating layer adjacent to the sourceregion, drain region and channel region; a floating gate elementadjacent to the electrically insulating layer, the electricallyinsulating layer separates the floating gate element from the channelregion; a control gate electrode adjacent to the floating gate element,the floating gate element separates the control gate electrode from theelectrically insulating layer, the channel region, electricallyinsulating layer, floating gate element and control gate electrode beingstacked in a vertical direction, the vertical direction beingperpendicular to the horizontal direction; and a magnetic field directedthrough the channel region and perpendicular to the vertical directionand the horizontal direction.
 2. A memory device according to claim 1,wherein the magnetic field alters an electron trajectory toward thefloating gate element.
 3. A memory device according to claim 1, whereinthe floating gate element is magnetic and the floating gate elementgenerates the magnetic field and the control gate electrode isnon-magnetic.
 4. A memory device according to claim 3, wherein thefloating gate element comprises a ferromagnetic pinned layer and ananti-ferromagnetic pinning layer.
 5. A memory device according to claim3, wherein the floating gate element comprises a syntheticanti-ferromagnetic element.
 6. A memory device according to claim 3,wherein the floating gate element is less than 100 Angstroms from thechannel region.
 7. A memory device according to claim 1, wherein themagnetic field is formed by a magnetic element, the magnetic element isadjacent to the memory device.
 8. A memory device according to claim 1,wherein the magnetic field is formed by an electrically conductive coil,the electrically conductive coil is adjacent to the memory device.
 9. Amemory device according to claim 7, wherein the magnetic element isadjacent to, but separated from the control gate electrode.
 10. A methodof writing to floating gate memory device, comprising: applying amagnetic field through a floating gate memory device to direct electronsin the device into a floating gate element of the floating gate memorydevice.
 11. A method according to claim 10, wherein the magnetic fieldis generated by a magnetic floating gate element and the control gateelectrode is non-magnetic.
 12. A method according to claim 11, whereinthe magnetic field is generated by a magnetic floating gate elementcomprising a ferromagnetic pinned layer and an anti-ferromagneticpinning layer.
 13. A method according to claim 11, wherein the magneticfield is generated by a magnetic floating gate element comprising asynthetic anti-ferromagnetic element.
 14. A method according to claim11, wherein the magnetic floating gate element is less than 100Angstroms from a channel region in the floating gate memory device. 15.A method according to claim 10, wherein the magnetic field is generatedby a magnetic element, the magnetic element is adjacent to the memorydevice.
 16. A method according to claim 10, wherein the magnetic fieldis generated by an electrically conductive coil, the electricallyconductive coil is adjacent to the memory device.
 17. A method accordingto claim 15, wherein the magnetic element is adjacent to, but separatedfrom a control gate electrode of the floating gate memory device.
 18. Amemory device comprising: a substrate having a source region, a drainregion and a channel region, the channel region separates the sourceregion and the drain region, electrons flow through the channel regionbetween the source region and the drain region; an electricallyinsulating layer adjacent to the source region, drain region and channelregion; a floating gate element adjacent to the electrically insulatinglayer, the electrically insulating layer separates the floating gateelement from the channel region; a control gate electrode adjacent tothe floating gate element, the floating gate element separates thecontrol gate electrode from the electrically insulating layer, thechannel region, electrically insulating layer, floating gate element andcontrol gate electrode being stacked in a vertical direction; and aplurality of magnetic particles within the channel region.
 19. A memorydevice according to claim 18, wherein the magnetic particles have aparticle size in a range from 1 to 6 nanometers.
 20. A memory deviceaccording to claim 18, wherein the magnetic particles comprise nickel orcobalt.